Outboard motors are generally designed to discharge exhaust from the engine downward through a genera11y hollow drive shaft housing and release the exhaust under water. During operation over most of the outboard motor's speed range, the exhaust is discharged at a low pressure region formed aft of the propeller. At idle and low speeds, however, the exhaust duct generally fills with water, necessitating an alternate path for exhaust flow. Examples of prior constructions which include exhaust relief systems are Hall et al, U.S. Pat. No. 4,507,092; Harrelson, U.S. Pat. No. 3,967,446; Boda et al, U.S. Pat. No. 3,350,879; Kollman, U.S. Pat. No. 3,310,022; and Hulsebus, U.S. Pat. No. 3,045,423.
While the prior systems are effective to relieve the exhaust pressure at low and idle speeds, it is generally desireable to provide a reduced level of exhaust noise at idle and low speed operation.